Exploring the Effect of Age on the Reproductive and Stress Physiology of Octopus bimaculoides Using Dermal Hormones

SIMPLE SUMMARY: Octopuses are charismatic animals commonly kept in aquaria and increasingly used for scientific research. As we begin to care for more of these animals in captivity, an understanding of how they perceive life in an aquarium is necessary to provide adequate welfare. Further, octopuses have a comparably short life span, averaging about 1–2 years. Due to these factors, it is necessary to learn more about how to care for these animals and increase their reproductive output while living in an aquarium. In this study, we validated a noninvasive technique to measure the glucocorticoids and reproductive hormones of the California two-spot Octopus, Octopus bimaculoides. We tested for differences in these hormones between reproductive and senescent (animals towards the end of their life) individuals. Reproductive individuals had higher sex hormone concentrations than senescent individuals, while the reverse was true for stress hormones. In terms of their stress response, reproductive individuals had a higher increase in glucocorticoids concentrations compared to their senescent counterparts after being exposed to a stressful event. These results provide a first step in broadening our ability to noninvasively collect hormones and expand our knowledge of how octopus hormones change throughout their lifetime. ABSTRACT: Our goal was to validate the use of dermal swabs to evaluate both reproductive and stress physiology in the California two-spot octopus, Octopus bimaculoides. Our objectives were to (1) use dermal swabs to evaluate glucocorticoids and reproductive hormones of O. bimaculoides; (2) determine the influence of life stage on hormone production (glucocorticoids in all individuals; testosterone, estrogen, and progesterone in females; and testosterone in males) of reproductive (n = 4) and senescent (n = 8) individuals to determine the effect of age on hormonal patterns; and (3) determine whether these hormones change significantly in response to an acute stressor. For the stress test, individuals were first swabbed for a baseline and then chased around the aquarium with a net for 5 min. Afterward, individuals were swabbed for 2 h at 15 min intervals to compare to the pre-stress test swab. Reproductive individuals responded to the stressor with a 2-fold increase in dermal cortisol concentrations at 15 and 90 min. Six of the eight senescent individuals did not produce a 2-fold increase in dermal cortisol concentrations. Reproductive individuals had significantly higher sex hormone concentrations compared to senescent individuals (progesterone and estradiol measured in females, and testosterone for both sexes). After the stressor, only reproductive males produced a 2-fold increase in dermal testosterone concentrations, while sex hormones in females showed no change. The stress hormone cortisol was significantly higher in senescent than in reproductive individuals, independent of sex. Dermal corticosterone concentrations were highest in senescent females followed by senescent males, and lowest in reproductive individuals regardless of sex. Dermal swabs provide an effective and noninvasive means for evaluating octopus hormones. Application of these indicators may be imperative as cephalopods are more commonly cultured in captivity for experimentation, display, and consumption.